1. Field
Example embodiments of the present inventive concepts herein relate to an electronic device and methods of fabricating the same, and more particularly, to an electronic device including a graphene thin film and methods of fabricating the same.
2. Related Art
Memory devices storing and reading information using a difference in current size according to the storage state of electric charges, electronic devices converting electricity into light (e.g., light emitting devices that covert electricity into light) or converting light into electricity (e.g., solar cells and photodetectors that convert light into electricity), etc., will be referred to as electronic devices throughout this disclosure.
Graphene is a material having a structure in which carbon atoms are two-dimensionally combined like graphite. Unlike graphite, however, the graphene is formed very thinly in a single layer, or in multiple-layers (e.g., two or three layers). Because graphene is flexible and transparent and has a high electrical conductivity, graphene is considered a promising material for use as a flexible electrode or a material for electron transfer in the next generation of electronic devices.
The use of graphene for forming an electron transport layer or a transparent electrode of an electronic device using the photovoltaic principle that converts light into electricity (similar to solar cells and photodetectors) is receiving great attention. While indium tin oxide (ITO) is being widely used to form transparent electrodes of electronic devices, the manufacturing costs associated with ITO have increased due to the increasing high costs and limited availability of indium (In). Furthermore, it is difficult to use ITO in flexible devices due to its lack of flexibility.
Typical methods for manufacturing a graphene thin film for transparent electrodes can be divided into methods for manufacturing a thin film by purifying graphite using a catalyst, and wet methods using graphene oxide. A method for manufacturing a graphene thin film by purifying graphite involves covering graphite adhered on a substrate with a catalyst, and then covering the resultant structure with polymers and performing a heat treatment to obtain graphene from graphite. Then, the substrate is removed, and a graphene thin film is obtained. A wet method using graphene oxide involves oxidizing graphene, mixing and diffusing the oxidized graphene in a solution, followed by spin coating the graphene solution to directly form an electrode or electron transport layer.
Methods that use graphite and a catalyst can be used to obtain a high-quality graphene thin film, but involve fairly complicated processing. Because methods that use oxidized graphene can use typical polymer processing (such as spin coating), the methods can easily form graphene thin films having a large surface area through fairly simple processes. However, because oxidized graphene is used, the electrical characteristics are inferior compared to the use of pure graphene. Because a thin film is formed in separate small pieces instead of a unified single thin film, the characteristics for a transparent electrode are inferior compared to a typical ITO.
Recently, there has been proposed a method of fabricating a device, which involves coating and heat-treating a polymer on a substrate to convert the polymer into graphene. Additionally, there has been proposed a method of fabricating a device, which involves supplying a vapor carbon supply source to grow graphene, then separating the graphene from the substrate to form a sheet-shape, and moving the graphene sheet to a device-substrate to manufacture a device. However, because graphene is very thin, graphene may easily be damaged when moving or handling the graphene in order to attach structures to on the graphene opposed to during the process of manufacturing graphene.
Accordingly, studies are being conducted on technology such as a method involving forming poly methyl methacrylate (PMMA) on manufactured graphene and then moving the PMMA and graphene layers onto a desired structure in order to move (or transfer) the manufactured graphene thin film onto the desired structure. This technology involves depositing PMMA on graphene over a substrate and simultaneously-separating the PMMA and graphene layers from the substrate by removing the substrate. Thereafter, the PMMA and graphene layers are attached onto a desired structure, and then PMMA is removed so as to prevent physical damage of the graphene. To this end, however, the entire process for manufacturing a device increases because an etching process for removing PMMA, after deposition of PMMA on graphene, is necessary. Also, graphene may be damaged in the course of chemically removing PMMA.